In this paper a finite element of beam-column joint is presented, which is intended to be employed in the nonlinear seismic analysis of r.c. frames. This should allow to include in the study of these structure the deformability of joints, which are instead assumed as rigid in the common practice. In this first approach the slippage of reinforcing bars is considered as prevailing on other sources of deformability. Good correlation has been obtained with experimental tests on beam-column joints.